Energy transfers

Question 1

Kinetic energy

Answer 1

Energy in moving objects, eg comets, runners and cars

Question 2

How to find kinetic energy?

Answer 2

Kinetic energy = 0.5 x mass x speed²

Question 3

Gravitational potential energy

Answer 3

Energy stored in a raised object

Question 4

How to find gravitational energy?

Answer 4

Mass x gravitational field strength x height

Question 5

Work done

Answer 5

This tells us the amount of energy transferred from one store to another to move an object

Question 6

How to calculate work done?

Answer 6

Force (N) x Distance (m)

Question 7

Power

Answer 7

The amount of energy transferred (or work done) per unit time

Question 8

How to calculate power?

Answer 8

Energy transferred or work done (J)
——————————————————
Time (s)

Question 9

Efficiency

Answer 9

A measure of how much energy transferred is used usefully and not dissipated into the surroundings

Question 10

How to calculate efficiency using power

Answer 10

Useful power output
——————————— x 100
Total power input

Question 11

How to calculate efficiency using energy transferred?

Answer 11

Useful energy output
——————————— x 100
Total energy input

Question 12

How can we increase the efficiency?

Answer 12

By reducing wasted energy transfers such as:
Using a lubricant to decrease friction
Using a lid to stop heat being dissipated when using a pan
When heating a pan, place the heating element inside so the heat doesn’t get lost to the base outside it
Use an insulating material such as plastic rather than a conductor such as metal

Question 13

How can we decrease heat transfers in a building?

Answer 13

Fill the cavity in between the wall with insulating material so heat cant transfer from inside to outside
Use double glazed windows so less energy can pass through
Use loft insulation to reduce heat transfers in a roof

Question 14

Conduction

Answer 14

Heating by vibrating particles spreading across a material
The kinetic energy in these vibrations causes heat transfers

Question 15

Convection

Answer 15

When particles with a lot of heat energy in a gas/liquid take the place of particles with little heat energy

Question 16

How do lava lamps work?

Answer 16

Through convection currents
When heat energy is transferred, the wax’s volume increased
This is because the particles inside move faster and the gaps each between the particles increase causing it to get bigger
The heated wax is less dense than the liquid water so it will rise
It will then cool at the top and become denser, thus sinking

Question 17

Unit for work done

Answer 17

Joules

Question 18

Unit of power?

Answer 18

Watts/ W

Question 19

Unit for work done?

Answer 19

Joules (J)

Question 20

If someone uses force on an object but it doesn’t move at all has any work been done to the object?

Answer 20

No because the equation is work = force x distance so if there’s no movement, there’s no distance and so no work done

Question 21

2 types of work done

Answer 21

Mechanical
Electrical

Question 22

Mechanical work done

Answer 22

Amount of energy transferred to cause an object to move

Question 23

Electrical work done

Answer 23

Current transferring electrical energy to its components eg electrical energy —> light energy in a lamp

Question 24

Is convection possible in solids?

Answer 24

No because for convection to take place the particles must be free to move to take the place